Citation. Hairston, A. B.; Grigal, D. F. 1994. Topographic variation in soil water and nitrogen for two forested landforms in Minnesota, U.S.A. Geoderma 64:125-138.   [1066  LTER]

Abstract. Relationships between topographic position and soil water, soil nitrogen ( N ) . and tree growth were examined on two regional landforms in Minnesota, USA. The study was conducted in northern pin oak stands (Quercus ellipsoidalis E.J. Hill) on an outwash plain, and in aspen stands (Populus tremuloides Michx.) on a ground moraine complex. Three slope positions (upper, middle, lower), four aspects (NE, SE, SW, NW) and concave and convex plan (across-slope) curvature were compared. Differences in soil water were significant (p < 0.05 ) among slope positions at both locations, but they differed more strongly in the subdued outwash plain than in the steeper moraine due to a shallow water table. Only soil water in lower slope positions in the moraine differed significantly between concave and convex across-slope shapes (p<0.05). In the outwash plain, organic matter and N of the upper soil horizon were related to slope position, while organic matter and total N in the forest floor and anaerobically released N in the upper soil horizon were related more strongly to aspect. In the moraine, N variables did not differ significantly by topographic position. In the outwash plain, tree growth rates differed by slope position and aspect; in the moraine, tree volume (but not growth rate) differed by slope position (p < 0.10) . Assumptions about differences in soil properties among topographic positions that are based on generalized models should be tempered by unique influences of landform and soil materials.